Serge, I'd ask your dealer to ask Meridian.
I know no Meridian dealer

Applying -10dB or -15dB on the sub channel is the norm for players with analogue outputs.
Yes. But i believe the Denon example is the good answer. They have split the LFE management in two part : analog domain/digital domain.
If you take a look at the G68 documentation :
Note: Multichannel analogue sources may have subwoofer level
outputs that vary by up to 10dB, so it may be necessary to reduce
the LFE level to give correct bass integration; see DSP presets, page
37.
Page 44 :
Cinema
The Cinema preset is recommended for listening to multichannel
movie soundtracks when no further processing is required.
Discrete
The Discrete preset is similar to Cinema, except that it uses the
Music speaker layout and sets the LFE level to -10dB.Meridian has choose the exact oppposite way to manage the LFE level in the case of an 5.1 analog input. (same thing in the last 861 documentation)
The management of the level in the player is just there to calibrate the speakers not to compensate the level differences between each sound format. This why it is not possible to add +15db on the LFE channel in the player (and the +15db is needed if you choose to do the bass management in the player)
Serge.